1. Field of the Invention
This invention is concerned generally with the maintenance of 2,3-diphosphoglycerate levels of red blood cells during extended storage, and specifically and a heat-sterilizable solution for achieving such storage.
2. Description of the Prior Art
Human blood is typically collected and processed using so-called multiple blood bags consisting of a medical grade plastic primary bag (for collecting whole blood from a blood donor) connected to one or more secondary bags into which various components of blood may be expressed for storage and later use. Examples of such multiple blood bags are shown in U.S. Pat. No. 3,064,647 to Earl and U.S. Pat. No. 4,195,632 to Parker et al. The introduction of multiple blood bag systems for blood collection and processing has made it possible for blood banks to supply an increasing range of blood components for transfusion. As a consequence, the processing of blood into components has increased dramatically. Because of this attention is being directed to methods of enhancing the storage properties of such components.
The first component removed from whole blood is platelet-rich plasma. This is obtained conventionally by centrifugation to separate the plasma and packed red cells. Such red cell preparations are replacing whole blood to an increasing extent in blood transfusion therapy. When plasma is removed from whole blood leaving a red cell concentrate, the increased viscosity of the concentrate makes rapid transfusion difficult and, accordingly, requires dilution (e.g., with a physiological saline solution) to flow properly. In addition, red blood cell concentrates lose glucose and adenine, and as a result, maintenance of a sufficient red blood cell ATP level may be difficult. Also, it is desirable to maintain the 2,3-diphosphoglycerate (2,3-DPG) level of red blood cells leading to improved red blood cell oxygen offloading characteristics.
When whole blood is drawn from a donor, it is commonly collected into a plastic blood bag containing an anticoagulant or preservative solution such as acid-citrate-dextrose (ACD), USP XX, page 49; citrate-phosphate-dextrose (CPD), USP XX, pages 49-50, CP2D which contains twice the amount of dextrose as CPD, Lovric et al, Med. J. Aust., 1977, 2, 183-186; or CPD plus adenine (CPDA or CPDA-1), Zuck et al, Transfusion, 17, 374-382 (1977). All of the above references are incorporated herein by reference. Whole blood collected into ACD or CPD can be stored for 21 days under conventional blood banking procedures, and red cell concentrates stored in ACD or CPD also remain viable for 21 days. The storage life of whole blood has been extended to about 35 days with CPDA-1 as the anticoagulant or preservative solution. However, storage of red cell concentrates for extended periods in CPDA is marginal (see Zuck et al, ibid.).
As mentioned above, dilution with a physiological saline solution has been used to enhance the flow properties of red cell concentrates. This introduces an extra handling step for clinicians, since the dilution step generally must be carried out shortly before infusion.
In attempting to overcome the above difficulties it has been reported by Lovric et al, The Medical Journal of Australia, 1977, 2, 183-186 that red blood cell concentrates may be stored for 35 days when mixed with an adenine-enhanced electrolyte solution containing trisodium citrate, citric acid, disodium hydrogen phosphate, dextrose, sodium chloride, and adenine. Hogman et al in Transfusion, 18, 233-241, 1978, and Hogman et al, The New England Journal of Medicine, 299, 1337-1382, 1978, reported the dilution of red blood cells, prepared from whole blood conventionally collected into a CPD-medium, with saline-adenine-glucose (SAG). The red cell concentrate mixed with SAG can be stored for a period of up to 35 days.
U.S. Pat. No. 4,267,269 discloses a storage solution for packed red cells which contains SAG plus mannitol. The solution contains, per 100 ml, 5-50 mg of adenine, 1000-3500 mg of glucose or fructose, 400-1200 mg of sodium chloride, and 250-2000 mg of mannitol.
Storage solutions for red cell concentrates containing dextrose, sodium dihydrogen phosphate, and mannitol with or without inosine and adenine are taught by Ginzburg in Bibl. Haemat., No. 38, part II, pp 217-220, 1971. Beutler ("The Red Cell in Vitro", Grum and Stratton, New York, N.Y., 189-216, 1974) and Wood et al (Blood, 42, 17-25, 1973) describe a red cell storage medium comprising sodium bicarbonate, sodium carbonate, sodium phosphate, adenine, glucose, and mannitol.
It is known that CPD adenine supplemented with sodium ascorbate and dihydroxyacetone improved maintenance of red cell 2,3-DPG during prolonged storage (Wood et al, Transfusion, 14, 272, 1974). Unfortunately, however, sodium ascorbate and ascorbic acid are unstable in aqueous solution. A stabilized derivative of ascorbic acid, ascorbate phosphate, has been evaluated in conjunction with dihydroxyacetone and CPD-adenine (Bensinger et al, Transfusion, 16, 518, 1976). It was shown, however, that ascorbate phosphate in aqueous solution at pH 5-8 was s degraded to an extent of about 25% upon autoclaving the solution at 121.degree. C. for 20 minutes. See the Bensinger et al article cited above. Moore et al, in Transfusion, 21, 723-731, 1981, have disclosed optional additive solutions. CPD-collected red blood cells in a solution containing adenine, glucose, and ascorbate phosphate or CPD-adenine collected red blood cells in a solution containing ascorbate phosphate have each indicated the potential to store red blood cells at least 42 days and to maintain red blood cell 2,3-DPG.
Unfortunately, however, the degradation of ascorbate phosphate during autoclaving or heat sterilization presents a substantial disadvantage to the use of ascorbate phosphate to maintain red blood cell 2,3-DPG. Such degradation not only reduces the effective amount of ascorbate phosphate but also results in degradation products which may be toxic.